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The size of the baffles dictate the actual limit of lofting. Some overstuffing can help compensate for humidity and dirt. JRB suggests not adding more than 20%. Beyond that, you're just adding weight and money for marginal to nonexistent returns.

DWR helps to keep the quilt from absorbing some moisture. Dew and some rain will bead off of the material whereas it would be absorbed directly into the quilt and insulation without it.

The size of the baffles dictate the actual limit of lofting. Some overstuffing can help compensate for humidity and dirt. JRB suggests not adding more than 20%. Beyond that, you're just adding weight and money for marginal to nonexistent returns.

DWR helps to keep the quilt from absorbing some moisture. Dew and some rain will bead off of the material whereas it would be absorbed directly into the quilt and insulation without it.

Simply multiply the fill power times the ounces of down then divide that result by the length, and width of the quilt. That will give you the effective loft. Each inch of loft is equivalent to approximately 18*F. Do this for the different amounts of fill that you are considering and you can then see the effect of overfilling.

For practical purposes, don't worry about any compression from over stuffing. You can compress down in half it's normal loft without degrading it's insulating properties.

Simply multiply the fill power times the ounces of down then divide that result by the length, and width of the quilt. That will give you the effective loft. Each inch of loft is equivalent to approximately 18*F. Do this for the different amounts of fill that you are considering and you can then see the effect of overfilling.

For practical purposes, don't worry about any compression from over stuffing. You can compress down in half it's normal loft without degrading it's insulating properties.

You'd need to include the baffle height into the equation as well since the volume is needed rather than just the area.

You'd need to include the baffle height into the equation as well since the volume is needed rather than just the area.

Actually you don't. It's insulation ability is determined not by the actual loft that is restricted by baffle height, but the effective loft that the volume of down would create if unrestricted. At least until you start doubling the compression.

Actually you don't. It's insulation ability is determined not by the actual loft that is restricted by baffle height, but the effective loft that the volume of down would create if unrestricted. At least until you start doubling the compression.

If you sew two pieces of fabric together to yield a 6"X40" chamber after allowing for the seam, that chamber would then be filled with down. Were the chamber to be completely filled, it will transform from a flat 6" wide two dimensional object into a cylinder. As the cylinder expands, the 6" dimension will contract until it becomes a circle. Two 6" pieces combine to make a 12" circumference. That 12" circumference will then yield a tube roughly 3.8" across.
Taking the radius of 1.9 squared X pi X 40, that will give you a Volume of 453 cubic inches ( roughly 1/2 ounce of 900 fill down) with no compression.

Now if I only took the length and width into consideration (in this case 40"X6"), how would I derive the amount of down required to fill the chamber without first calculating the volume?

yeah your kinda doing it backwards Mad but your not totally wrong .. the formula is LxWxH/fill (LengthxWidthxHeight or baffle height /Fill power of your down) you need 3 point to calculate how much down you need to fill a set amount
the same goes for air space as well(speaker box)... you need 3 point to determine the outcome what your doing is determining the size of baffles needed for a set amount of fill not loft it's almost the same thing as above but it's easier to determine a set amount with a set baffle height IMO (or 3 points)
your kinda doing something we call the Ohm's law in electronics where you can take voltage,ohm's or some say resistance,current you can flip flop them to determine any of the 3... pretty much what your doing...also loft is a byproduct of down there is no true way to calculate how much loft you will get in any given UQ could be 3 inch ...could be 3 1/4 ..

wisenber is dead on with baffle height your down can only produce so much loft with the air space given .... so if your baffles are 3 inch... your not going to get 5inch of loft no matter how much you stuff it.. you also need to take in affect when a person os laying in the hammock and putting pressure against the UQ ... this will take away from the loft as well even with a Diff. cut you still will lose some so overfill can be good to a point but too much is a waste of weight IMO i always felt 2oz of overstuff was more than plenty thats just me
not saying this is the end all ... but from what i gathered over the years this is what i learned maybe a vendor will chime in or grizz he is a math wiz

I think what i'm trying to get at is your both right ..... just going about it different ways

It puts the Underquilt on it's hammock ... It does this whenever it gets cold

A lot of overstuff in a top quilt can make it stiffer, so it doesn't drape as well. The air spaces left between you and the quilt take a while to warm up, so it doesn't feel warm as quickly as one that drapes well. It may eventually be just as warm, but I don't know. It may not perform as well when you shift position (again, not sure). Feeling warm immediately is nice.